A magnetic sensor device is a sensor device that uses a magnetoresistance effect element having a characteristic whereby its resistance value changes corresponding to a magnetic field strength. The magnetization amount of the magnetic pattern of a paper medium such as paper money is subtle. In order to improve sensitivity to detect the magnetic pattern of an object to be detected whose magnetization amount is subtle, the magnetic sensor device needs to be configured in such a way that the magnetic sensor device uses an anisotropic magnetoresistance effect element, which has a higher detection sensitivity than a semiconductor magnetoresistance effect element, and the anisotropic magnetoresistance effect element is disposed under a magnetic field strength in which sensitivity is the highest, and the object to be detected passes through a ferromagnetic field.
However, in a magnetic sensor device using an anisotropic magnetoresistance effect element, the anisotropic magnetoresistance effect element is saturated at a magnetic field strength of about 10 mT. Therefore, there is a problem in that it is difficult to dispose the anisotropic magnetoresistance effect element in a magnetic field strength environment in which the anisotropic magnetoresistance effect element is not saturated and the detection sensitivity is the highest.
In addition, in a non-contact magnetic sensor device, the object to be detected such as a paper sheet medium and a magnetoresistance effect element are apart from each other by a predetermined distance, making smaller an output of change in the resistance value of the magnetoresistance effect element which, in turn, causes deterioration of detection sensitivity.
In order to solve such a problem, Patent Literature 1 discloses a magnetic sensor in which the position of a permanent magnet is adjusted so that the bias magnetic field strength in the magnetic sensing direction of the ferromagnetic thin-film magnetoresistance element applied by a detecting magnetic field by the permanent magnet has a magnetic flux amount of a saturated magnetic field or lower.